Transcriptome Analysis Uncovers a Link Between Copper Metabolism, and Both Fungal Fitness and Antifungal Sensitivity in the Opportunistic Yeast Candida albicans

Abstract

Copper homeostasis is an important determinant for virulence of many human pathogenic fungi such as the highly prevalent yeast Candida albicans. However, beyond the copper transporter Ctr1, little is known regarding other genes and biological processes that are affected by copper. To gain insight into the cellular processes that are modulated by copper abundance in C. albicans, we monitored the global gene expression dynamic under both copper depletion and excess using RNA-seq. Beyond copper metabolism, other different transcriptional programs related to fungal fitness such as stress responses, antifungal sensitivity, host invasion and commensalism were modulated in response to copper variations. We have also investigated the transcriptome of the mutant of the copper utilization regulator, mac1, and identified potential direct targets of this transcription factor under copper starvation. We also showed that Mac1 was required for the invasion and adhesion to host cells and antifungal tolerance. This study provides a framework for future studies to examine the link between copper metabolism and essential functions that modulate fungal virulence and fitness inside the host.

Expanded role of the Cu‐sensing transcription factor Mac1p in Candida albicans

“…We observed strong induction of genes involved in reductive Fe uptake, heme acquisition, and the siderophore transporter SIT1 (Figure 4a), all of which are known be induced under Fe starvation stress conditions (Chen et al, 2011). While this manuscript was in its final stages of preparation, Khemiri et al published a study showing a similar high induction of specific Fe transport genes in mac1∆/∆ cells from the background strain SN125 (Khemiri et al, 2020).…”

“…albicans , other genes downregulated by BCS but not in mac1∆/∆ mutants include AAH1 , which encodes an adenine deaminase (Uhl et al ., 2003; Garcia‐Sanchez et al ., 2005), and FGR23 , implicated in the regulation of filamentous growth (Uhl et al ., 2003) (Figure ). Neither AAH1 or FGR23 are predicted to encode cuproproteins, nor contain consensus sequences for Mac1p binding (Woodacre et al ., 2008; Khemiri et al ., 2020) downstream of the start site as is the case for SOD1 (Li et al ., 2015), or in upstream promoter sequences. It is therefore possible that SOD1 is the only gene repressed by Mac1p in C. albicans , highlighting the importance of SOD1 repression during Cu starvation.…”

“…Thus, Mac1p plays an important role in fungal virulence in disseminated candidiasis. Recent studies by Khemiri have shown role for C. albicans Mac1p in adherence to a human colon epithelial cell line in vitro, consistent with the importance of Mac1p in fungal growth and cell invasion (Khemiri et al ., 2020).…”

“…Such genes should be upregulated upon treatment with BCS but not in mac1∆/∆ strains. Indeed, we identified many known targets of Mac1p including genes for Cu uptake ( CTR1, FRE7, FRE30 ), and genes that substitute for Sod1p loss ( SOD3, AOX2 ) (Figure ) (Woodacre et al ., 2008; Li et al ., 2015; Khemiri et al ., 2020). Additionally genes encoding hexose sugar transporters and hyphal‐specific genes (e.g., ECE1, HWP1, ALS3 ) were among those uniquely induced by BCS (Figure and Table ); none of which contained obvious Mac1p binding consensus sequences.…”

“…Neither AAH1 or FGR23 are predicted to encode cuproproteins, nor contain consensus sequences for Mac1p binding (Woodacre et al, 2008;Khemiri et al, 2020) downstream of the start site as is the case for SOD1 (Li et al, 2015), or in upstream promoter sequences. It is therefore possible that SOD1 is the only gene repressed by Mac1p in C. albicans, highlighting the importance of SOD1 repression during Cu starvation.…”